1. Field of the Invention
This invention generally relates to equipment used for well completion, re-completion, or workover. In particular, this invention relates to frac ball injector assemblies and control systems used to drop or launch frac balls into a wellbore to facilitate completion operations for oil and gas wells.
2. Description of Related Art
Hydraulic fracturing (“fracing”) is a commonly used technique to increase the production of oil and natural gas wells. In combination with horizontal drilling, this technique allows manufacturers to extract large amounts of hydrocarbons stored within shale in an economically feasible manner. Prior to the fracing process, a drilling company will typically drill a hole first vertically several thousand feet to the depth of the gas and oil bearing reservoir and then horizontally along the shale layer. Subsequently, the wells are lined with steel pipe (“casing”) that is inserted into the well bore. The casing is perforated at target zones so that a liquid can be injected at high pressures into the surrounding shale such that the liquid creates small cracks or fractures in the shale to expose the trapped hydrocarbons. The shale is typically fractured in sections, with the horizontal area furthest from the well bore being fractured first. Subsequently, that section is isolated and the next section is fractured. In this way, through multiple fracturing and isolation steps, i.e., multi-stage fracing, the complete horizontal section is fractured from the end of the well to a predetermined location closest to the well bore.
One method of isolating various sections or exposing perforations in the casing to accomplish multi-stage fracing is by using frac-balls. Frac-balls are spheres made of various materials such as ceramic, G10/FR4, a thermosetting industrial fiberglass composite laminate, or injection molded composite thermoplastic or phenolic resin. The balls are launched from the surface into the well bore in a predetermined order and land in seats, having a diameter smaller than that of the ball, at predetermined locations in the pipe. The balls isolate a portion of the well that has already been fractured by preventing or restricting incoming fluid from reaching those portions of the well. Further, by seating the balls in sleeves the seats can be translated to expose perforations in a portion of the liner. These perforations allow fracing fluids to be injected into that portion of the well behind the ball to fracture those regions of shale.
Typically, the well is fractured starting with the horizontal region furthest away from the vertical well bore, working back towards the surface. Multiple balls can be launched in one completion operation. One or multiple balls having a small diameter are first launched, isolating the first portion of the well and/or opening perforations. Following the fracturing operation of that portion of the well, balls having increasing diameter are subsequently, sequentially launched, and fracturing operation of the remaining portions are conducted in the same completion operation.
While it is possible to manually drop a ball into the fluid flow, this method is time consuming, prone to human error, and requires workers to be located close to high-pressure areas, thereby presenting safety concerns. Ball launchers, affixed to the well, allow balls to be preloaded and subsequently injected into the fluid flow, to be carried into the well. Multiple ball launchers can be used in a multi-step fracturing operation without breaking high-pressure connections, allowing completion operations to proceed efficiently. However, inadvertent launching of a ball or improper sequencing of the balls remains a problem. Balls launched improperly can result in additional time and expense for removing the ball and reworking well completion operations.
Thus, there is a need in the art for a reliable frac ball launching unit capable or launching multiple balls while reducing the possibility of inadvertent or improper launching or improper sequencing of balls.